1) Field of the Invention
The present invention is for the purpose of forming a film-like or sheet-like resin-made membrane (signifying a thin-film), and relates to a resin-made membrane formation casting apparatus suitably used, for example, as a biaxial oriented film machine, a non-oriented film machine, a sheet machine, and others.
2) Description of the Related Art
FIGS. 31 and 32 are respectively a side elevational view and a front elevational view each illustratively showing a prior resin-made membrane formation casting apparatus. Although FIG. 32 shows only one end portion side of the prior apparatus in its width direction, the other end portion side is constructed in a similar way.
As shown in FIGS. 31 and 32, the prior apparatus is equipped with a T die 101 for extruding a molten resin from an extruding machine (not shown) into a film-like or sheet-like membrane 102, a casting roll (cooling roll) 103 for receiving the membrane 102 extruded from the T die 101 on its outer circumferential surface to cool and deliver the membrane 102, and a suction chamber (vacuum box) 104 for stably making the membrane 102 come closely into contact with the surface of the casting roll 103.
In this constitution, the casting roll 103 is supported by a roll supporting shaft 106 to be rotatable with respect to a side frame 107.
The suction chamber 104 is fixedly secured on one side surface of the T die 101. Further, a vacuum pump 105 is in a coupled relation to the suction chamber 104 so that, when this vacuum pump 105 is placed into operation, the air between the membrane 102 and the casting roll 103 is sucked through an opening section 104a of the suction chamber 104.
The opening section 104a is made throughout the overall width of the membrane 102 in the proximity of a portion where the membrane 102 starts to come closely into contact with the outer circumferential surface of the casting roll 103. Further, a seal gap 104b is defined between the suction chamber 104 and the casting roll 103. The dimension of the seal gap 104b is set to ensure a required suction force (pressure reduction level) at the close contact section between the membrane 102 and the casting roll 103 concurrently with allowing the rotation of the casting roll 103. In FIGS. 31 and 32, reference numeral 108 represents wheels to be used when shifting this apparatus.
With the above-mentioned constitution, the resin molten by the non-shown extruding machine passes through the T die 101 to be extruded into a film-like or sheet-like membrane 102 which in turn, is placed on the outer circumferential surface of the casting roll 103 to be cooled for formation.
At this time, the air within the suction chamber 104 is sucked by the vacuum pump 105 so that the air in the close contact section between the membrane 102 and the casting roll 103 is sucked through the opening section 104a of the suction chamber 104. Whereupon, that close contact section is pressure-reduced to discharge the air taken in between the membrane 102 and the casting roll 103, with the result that the membrane 102 made of the molten resin can stably be brought into contact with the casting roll 103.
In this case, depending upon the kind of resin, on the condition that an interval between the T die 101 and the casting roll 103 is small, the orientation of the molten resin due to its extension is not relieved, but the resin is cooled and solidified on the casting roll 103, and hence, a necessary film characteristic (membrane characteristic) is unobtainable. In addition, under the condition that the interval between the T die 101 and the casting roll 103 is small, the microscopic surface irregularities occurring at the exit of the T die 101 is unreducible in the extension interval, and after being cooled and solidified, they remain as the surface roughness, thereby deteriorating the film quality (membrane quality).
Accordingly, a way of varying the interval between the T die 101 and the casting roll 103 in accordance with kinds of resins can be taken in order to attain the necessary film characteristic (membrane characteristic). However, in the prior apparatus shown in FIGS. 31 and 32, since the suction chamber 104 is fixed with respect to the T die 101, difficulty is encountered to vary the interval between the T die 101 and the casting roll 103.
For instance, even if, in the prior apparatus shown in FIGS. 31 and 32, the casting roll 103 is lowered to enlarge the interval between the T die 101 and the casting roll 103, the seal gap 104b between the suction chamber 104 and the casting roll 103 results in enlargement to make it difficult to obtain a necessary suction force, so that the removal of the air taken in between the membrane 102 and the casting roll 103 becomes impossible, with the result that it is impossible to stably make the membrane 102 come closely into contact with the casting roll 103.
Furthermore, according to an experiment, in the case of forming the membrane 102 through the use of a casting apparatus based upon the above-mentioned suction chamber 104, the configuration of the vacuum space defined by the membrane-like molten resin immediately after being discharged from the T die 101, the outer circumferential surface of the casting roll 103 and the tip portion of the suction chamber 104, or the occurrence or non-occurrence of the flow of the outside air into that vacuum space, has influence on the stably closely contacting condition of the membrane 102 with the casting roll 103 in accordance with the conditions such as the kind of resin material being, the resin viscosity when molten, the thickness of the membrane 102 and the formation speed. Particularly, in the case of a resin with a relatively low extension viscosity, the outside-air flow situation into the vacuum space affects the stably close contact of the membrane 102 with the casting roll 103.
For this reason, troubles take place; for example, the membrane 102 vibrates (swings) or is brought into the interior of the suction chamber 104, and particularly in the case of high-speed formation of the membrane 102, that influence becomes more serious. For example, FIG. 33 shows an outside-air inflow situation (the dotted arrows denote air flows) in a cross section taken along a line S--S of FIG. 31, and, as shown in FIG. 33, the membrane 102 vibrates (swings) or is brought into the interior of the suction chamber 104 due to the occurrence of the dynamic pressure at a portion designated at B2 and the eddy caused by the suction at a portion depicted at B1, which hinders the speed-up of the membrane formation.